Automatic volume control system



Feb. 7, 1933.

E. R. HENTSCHEL AUTOMATIC VOLUME CGNTROL SYSTEM FiledOct. 25, 1930 4 IN VEN TOR. @zm ar 5R. aewrwgw,

ATTORNEY 2 Patented Feb. 7, 1933' UNITED STATES PATENT OFFICE I ERNEST It. HENTSCHEL, OF WASHINGTON, DISTRICT OF COLUMBIA; JOHN OLSON AD MINISTRATOR or sAn) ERNEST a. HENTSCHEL, DECEASED, ASSIGNOR TO WIRED H RADIO; 1110., or NEW YORK. N. Y., A CORPORATION or DELAWARE AUTOMATIC VOITUME CONTROL SYSTEM Application filed October 23,1930. Serial No. 490,790.

invention relates broadly to automatic volume control systems for radio broadcast receive-rs and more particularly to a circuit arrangement for radio broadcast receivers by whichthe detrimental effects of fading may be materially reduced.

One of the objects of my invention is to provide means for reducing the effects of fading in the sound reproducer of a radio broadcast receiver by controlling the effective resistanceof the radio frequency amplification circuits of the receiver.

Another object of my invention is to provide a circuit-arrangement for a radio broadcast receiver wherein resistance is introduced into the amplification circuits of the receiver for compensating for fading effects and the effectivevalue of such resistance controlled by regulating the regenerative amplification of thecircuits of the broadcast receiver.

Other and further objectsof my invention reside inthe circuit arrangement for introducing resistance into the amplification circuits and simultaneously controlling the effective resistance by regenerative action as will be more fully set forth in the specification hereinafter following by reference to the accompanying drawing which diagrammatically illustrates a radio broadcast receiver embodying the principles of my invention.

,, In the circuit arrangement of my invention, I provide means for modifying the ef-. fective resistance of the amplification system for compensatingfor the effects of fading in the radio broadcast receiving circuits While reducing theefi'ective resistance of the tuned circuits by controlling the regenerative amplification of the system. My invention makes use of the' principles set forth more fully in my copending application Serial No. 462.904, filed June 21, 1930. In my aforesaid application,- the effective resistance of the amplification circuits is controlled by varymg the conductivity of a resistance member in the resonant circuits of the amplifier. The variation in resistance is effective through a circuit extending from the output system of the receiver whereby changes in amplitude of the incoming signaling energy due to the effects fading and other phenomena may be compensated by regulation of the effective i resistance of the amplification system. -Resistance elements disposed in circuit with the resonant systems of the amplification circuit are varied in their conductivity, by virtue of the thermal characteristics thereof under control of current derived fromthe incoming signaling energy so that rises in the amplitude of the incoming signaling energy such as occurs under conditions of fading tends to increase the resistivity of the resonant circuits and thereby maintain the volume of reproduced sound at a substantially uniform level. In order to overcome the effects of the resistance which is introduced into the resonant-circuits of the receiver, I provide means for controlling the regenerative amplification of the amplification circuits. The regenerative amplification control is provided in each amplification stage and the amount of signaling energy normally lost by reason of the introduction of resistance elements in the resonant circuits compensated for by the reamplification effect obtainable through the regenerative amplification paths in each amplifier stage. In this way, the introduction of resistance elements in the resonant circuits of the amplifier does not reduce the normal reception although permitting immediate control of the volume of the received energy under conditions of fading where the signaling energy may tend to rise in amplitude.

I Referring to the drawing in detail, reference character 1 designates the first stage of radio frequency amplification in a radio broadcast receiver which is'connected to the second stage of radio frequency amplification indicated at 2 which connects to the electron tube detector 3 which in turn connects to the audio frequency amplifier stage indicated at 4. The radio broadcast-receiver is connected to an antenna ground system designated at 5 and 6 connected in series with the primary winding 7 of the coupling transformer 8 having secondary winding 9 connectedtothe input circuit of the radio frequency amplifier stage 1. The output circuit of the radio frequency amplifier stage 1 connects through coupling transformer 10 ignated at 2. The resonant circuit which connects to the first stage of radio frequency amplification is designated generally at 14 including variable condenser 15, the resistance bridge circuit 16, and condenser 17 in shunt with the secondary inductance 9. The second resonant circuit which is-located in the input system 18 of the radio frequency amplification stage 2 includes V3. riable condenser 19, resistance bridge 20 and condenser 21 in shunt with the secondary winding 12 of coupling transformer 10. The

output circuit of the second stage of radio frequency amplification 2 connects through coupling transformer 22 to the input of the detector tube 3. The input circuit of the detector tube 3 is tuned by means of variable condenser 23. The output of the detector tube 3 is connected through audio frequency transformer 24 to the input of the audio frequency amplifier stage 4. The output of the audio frequency amplifier 4 connects through transformer 25 to the sound reproducer 26.

The power supply for the amplifier system is obtained from the alternating current line wire system shown at 27. The transformer 28 connects to the line wire system 27 and delivers energy to the rectifier 29 and thence to the filter system 30 to the potentiometer 31. Taps are taken from potentiometer 31 to the several circuits of the receiving apparatus and to the circuits of the rectifier 32 and direct current amplifier constituted by electron tubes 33 and 34. The rectifier 32 has its input circuit connected to the tuned circuit 35 which is coupled with winding 36 in the output circuit of the second stage of radio frequency amplification including elec tron tube 2. The winding 36 is independent of the primary winding 22a of the coupling transformer 22 which transfers energy to the detector 3. The rectifier tube 32 is conductively coupled with tubes 33 and 34 constituting the direct current amplifier stages which impress energy upon the resistance bridges 16 and 20.

In order to reduce the effective resistance of the tuned circuits 14 and 18, I provide paths for the passage of regenerative energy. Each regenerative path includes impedance devices. The first regenerative path includes inductance elements 37 and variable capacity 38 connected between the plate electrode of electron tube 1 and the cathode of electron tube 1 with the inductance 37 in inductive relation with the secondary inductance 9 of coupling transformer 8. The

second regenerative path includes the inductance 39 and variable condenser 40 connected between the plate electrode and the cathode of electron tube 2, the inductance 39 being coupled with the secondary winding 12 of coupling transformer 10. Energy is supplied in the first amplification stage through variable condenser 38 which is so adjusted that the energy supplied to the tank circuit 14 makes the efiective resistance of the tank circuit extremely low. The effective resistance of tank circuit 18 is overcome by the regenerative feed back of energy in the path including condenser 40 and inductance 39 regulated by the adjustment of condenser 40. The terminals of tuned circuit 35 connect to the input of the rectifier 32 which in turn couples to the direct current amplifier constituted by tubes 33 and 34, the output of which is delivered to the resistance bridge circuits 16 and 20 disposed in series as shown. Radio frequency choke coils 41 and 42 are connected in circuit with the resistance bridge 16. Radio frequency choke coils 43 and 44 are connected in series with the resistance bridge 20. The rectifier 32 is so biased that no current will be allowed to pass until the amplitude of radio frequency energy in coil 36 exceeds a predeterminedvalue. In this manner, no energy is withdrawn from the receiver circuit until this amplitude of energy exceeds a predetermined level. Condensers 17 and 21 in the first and second radio frequency stages are placed in the circuit in order to enable resistance bridges 16 and 20 to carry the plate potential of D. C. amplifier tube 34. This is for the purpose of keeping this higher potential away from the grid circuits of the radio frequency amplification stages.

The heating elements for all of the electron tubes are energized from secondary winding 45 on transformer 28. The amplification characteristic of the receiving circuit according to my invention is not impaired by the introduction of the resistance bridges 16 and 20 for the compensating action obtainable through the shunt paths between each of the tubes constituting the amplification stages eliminate effective resistance which is otherwise present bythe inclusion of the resistance bridges in the resonant circuits.

While I have described my invention in one of its preferred embodiments I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In an automatic volume control system for radio receivers, a receiving circuit including a radio frequency amplifier, a detec- .tor, an audio frequency amplifier and a sound pensating for the effect of said resistance in.

said resonant circuit.

2. In an automatic volume control'system for radio receivers, the combination of a receiving circuit, a resonant circuit connected therewith, a radio frequency amplifier having its input connected with said resonant circuit, a resistance element disposed in said resonant circuit, means interconnecting the output of saidradio frequency amplifier with said resistance element for modifying the effective value of said resistance element according to the amplitude of the incoming signal energy, and means connected with the radio frequency amplifier for normally compensating for the effects of said resistance in said resonant circuit.

3. In an automatic volume control system for radio receivers, a receiving circuit, a resonant circuit connected therewith, a radio frequency amplifier having its input connected with said resonant circuit, a resistance ele- -ment disposed in series with said resonant circuit, means for delivering energy from the output of said radio frequency amplifier to said resistance element for modifying the effective resistance thereof according to the amplitude of the incoming signaling energy, and means for feeding back energy from the output to the input of said radio fre uency amplifier for overcoming the normal e ect of the resistance element in said resonant circuit.

4. In an automatic volume control system for radio receivers, a signal receiving circuit, a multistage radio frequency amplifier system, a detector, an audio frequency amplifier, a sound reproducer connected with said audio frequency amplifier, resonant circuits interposed between each of said stages of radio frequency amplification, a resistance element connected in series with each of said resonant circuits, a circuit including the output circuit of the final stage of radio frequency amplification and each of said resistance elements in series, and means connected with each of said stages of radio frequency amplification for compensating for the normal effects of the resistance elements in each amplification stage.

5. In an automatic volume control system.

for radio receivers, a signal receiving circuit, a multistage radio frequency amplifier system, a detector, an audio frequency amplifier, a sound reproducer connected with said audio frequency amplifier, resonant circuits interposed between each of said stages of radio frequency amplification, a resistance element disposed in each of said resonant circuits, 9'. series connected path extendingbetween the output circuit of the final stage of radio frequency amplification and each of the resistance elements in said resonant circuits, and regenerative amplification paths interposed between the output and input of each of said amplification stages for compensating for normal effects of said resistance elements in said resonant circuits.

6. In an automatic volumecontrol system for radio receivers, a signal receiving circuit, a multistage radio frequency amplifier system, a detector, an audio frequency amplifier, a sound reproducer connected with said audio frequency amplifier, resonant circuits interposed between each of said stages of radio frequency amplification, a resistance element disposed in each of said resonantcircuits, a series connected path extending between the output circuit of the final stage of radio frequency amplification and each of said resistance elements in series, and separate paths connected between the output and input circuits of each of said amplification stages, said last mentioned paths including an inductance regeneratively coupled with the associated resonant circuit for effecting a regenerative amplification of ener for compensating for the effects of the resistance elements in said resonant circuits.

7. An automatic volume control systeni frequency am lifier and said resistance element for varylng the conductivity of said resistance element according to the amplitude of the incoming signaling energy, and a regenerative path between the output circuit of said radio frequency amplifier and the input circuit thereof, said path includingan inductance coupled with said resonant circuit and a variable capacity for controlling the feed back of energy between said output and input circuits for compensating for the normal effect of said resistance element in said resonant circuit.

8. In a signal receiving system, a signal re-. ceiving circuit, a resonant circuit including inductance and capacity elements connected therewith, a radio frequency amplifier including an input circuit and an output circuit, connections between said resonant circuit and the input circuit of said radio frequency amplifier, a resistance element interposed in said resonant. circuit, connections between the output circuit of said radio frequency amplifier and said resistance element for varying the conductivity thereof according to the amplitude of the incoming signaling energy, and a path connected between the output and input circuits of said radio frequency amplifier, said path including a variable capacity element and an inductance coupled With the inductance of said resonant circuit for effecting a feed back of energy in said radio frequency amplifier for compensating for the normal effect of the resistance element in said resonant circuit.

In testimony whereof I affix my signature.

ERNEST R. HENTSCHEL. 

